Integrally cast bearing, method and apparatus for making same

ABSTRACT

The invention relates to a process for forming a part including a bore with a bearing integrally cast thereto, the thus formed part and apparatus for thus forming the part. The process includes hot machining a bore into a billet in a non-oxidizing atmosphere and introducing molten bearing material, e.g., molten bronze about a mandrel positioned in the bore while maintaining the billet, the mandrel and the bearing material in the non-oxidizing atmosphere. The mandrel is drawn from the bore while the bearing material is cooled by cooling and solidifying means therein adjacent an end of the mandrel which is last to exit the bore. The cooling is sufficient to progressively solidify the material as the mandrel is drawn through it and out of the bore. The mandrel further preferably includes heating means therein intermediate the cooling and solidifying means and the other end thereof to maintain the material in a liquid state until the cooling and solidifying means passes there adjacent as the mandrel is drawn out of the bore.

BACKGROUND OF THE INVENTION

The invention relates to a process for forming a part including a borewith a bearing integrally cast therein. The invention also relates tothe resulting bearing and to a mandrel and to associated apparatusparticularly adapted to produce such a bearing. Such bearings areparticularly useful in track rollers utilized with heavy duty earthmoving equipment.

Track rollers on track type tractors typically utilize a pair of suchbearings to absorb both radial and axial loads, which in such equipmentcan be severe. Each bearing takes the form of an axially directed sleeveportion to which is joined a radially directed flange portion. Thebearings rotatably support a track roller on a shaft such that bothradial and axial loads are satisfactorily accomodated.

Some prior art bearings have taken the form of integrally cast unitswherein the entire bearing includes a sleeve portion which transcends toa radial flange or thrust surface portion. These prior art bearings havenot proven to be entirely satisfactory in view of the relatively highcost incidental to casting the integral thrust surface portion. Also, ithas been generally necessary to heat up the part to which the bearing isto be cast after the part has been formed and quenched to a desiredhardness.

One solution to this problem is the construction described in U.S. Pat.No. 3,624,881, issued Dec. 7, 1971 to Brown et al and assigned to theassignee hereof. This solution takes the form of a two piece bearingjoined into a unitary whole by the process of friction welding.

A problem with a friction welding construction is engendered by thenecessity of properly indexing the bearings within their supportingbushings so as to insure alignment of the oil holes in their respectiveelements. While this is not a problem in all cases, it is in some, andmore particularly in the cases where small shafts are concerned. Anotherproblem is that a failure to provide alignment of the oil holes betweenthe oil reservoir containing support bushing and the bearing will tendto cut off the supply of necessary lubricant and result in damage to thebearing, bushing and shaft.

Another solution to the problem is the construction described in U.S.Pat. No. 3,795,428, issued Mar. 5, 1974 to Paine et al and assigned tothe assignee hereof. This solution takes the form of a two pieceinterlocked support/thrust bearing. The interlocking means serves tojoin the pieces into a unit and also serves to prevent relative rotationbetween the pieces.

Problems with the two piece interlock support/thrust bearings areengendered by the care that must be taken to make them interlocking andthe inherent cost in so formulating them. Also, costs of assembly aresomewhat higher than desirable. Finally, under the very high weight ofmodern-day track roller utilizing vehicles, larger and more durabletrack roller bearings are desirable, as are inexpensive methods andapparatus to formulate them.

Accordingly, it is an object of the present invention to provide aninexpensive process for forming a rugged part such as a roller bearing,wherein the bearing is integrally bonded to the bore of a track rollerand wherein production of the part is relatively inexpensive in that itrequires only a single heating of a billet from which the part isformed.

SUMMARY OF THE INVENTION

In one sense, the invention comprises a process for forming a partincluding a bore with a bearing therein. The process comprises hotmachining a bore into a billet in a non-oxidizing atmosphere. Moltenbearing material is introduced about a mandrel positioned in the borewhile the billet, the mandrel and the bearing material are maintained inthe non-oxidizing atmosphere. The mandrel is drawn from the bore whilethe bearing material is cooled adjacent an end of the mandrel whichexits the bore last sufficiently to progressively solidify the materialas the mandrel is drawn through the material and out of the bore.

In another sense, the invention comprises a part, including a boretherethrough and a bearing solidified and bonded to said bore, said partbeing produced by the process described immediately above.

In yet another sense, the invention comprises a mandrel positionable ina bore, a bore facing surface of said mandrel being adapted to be spacedfrom said bore a distance generally equal to the thickness of a moltenmaterial to be cast onto said bore. The mandrel comprises cooling andsolidifying means therein, adjacent the one end thereof which exits saidbore last when said mandrel is drawn therefrom, to progressively cooland solidify said material as said mandrel is drawn out of said bore.The mandrel further includes heating means therein intermediate saidcooling and solidifying means and the other end thereof to maintain saidmaterial in a liquid state until said cooling and solidifying meanspasses through adjacent as said mandrel is drawn out of said bore.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the drawings,wherein:

FIG. 1 illustrates in a cross-sectional view a track roller and bearingof the present invention to which an integrally cast bearing has beenattached by the method of the present invention;

FIG. 2 illustrates in flow diagram the steps involved in the method ofthe present invention for integrally casting a bearing; and

FIG. 3 illustrates in a sectional view in a vertical plane a trackroller with the apparatus of the present invention for integrallycasting the bearing thereupon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A track roller 10 as shown in FIGS. 1 and 3 includes a pair of chainsupporting treads 12 and guide flanges 14 that are supported by anintegrally formed hub portion 16 which has an axial bore 18. At the endsof the bore and of an integrally formed bearing 19 are a pair ofrelieved end surfaces 20 which afford suitable means for rotatablysupporting the roller and mounting necessary seals and thrust bearings,not illustrated, thereto.

FIG. 2 illustrates in a typical flow diagram a preferred embodiment ofthe process for producing a track roller or a like part with a bearingcast integrally therein. The steps shown within the L-shaped box 21,namely the steps of heating 22, forging 24, machining 26 and pouring ofthe bearing 28 are each accomplished in a protective, controlledatmosphere. The protective controlled atmosphere is a non-oxidizingatmosphere which prevents oxidation of the surface to which the bearingis to be cast, so that efficient and integral sealing of the bearing 19to the bore 18 results. The prevention of oxidation insures a completebond between the bearing and the bore.

A billet of the proper size to produce the desired roller 10 is heatedto a forging or forming temperature (generally 650° to 1500° C) in theheating step 22. At this temperature the billet is readily formed bydies in the forging step 24 into a desired shape, e.g., that of thetrack roller. The forging or forming takes place, as illustrateddiagramatically, by the box 24. The still-hot part is then hot machinedin the machine step 26 by boring, broaching, or the like to produce thebore 18 against which the bearing 19 is to be cast. Other machining mayalso take place in the machine step 26, such as finishing of the endsurfaces 20 and the like. The machining is generally accomplished at atemperature above the melting point of the bearing material from whichthe bearing is to be formed.

After the forming and machining steps 24 and 26 are completed, thebearing 19 is cast by pouring a bearing material into the part and abouta suitable mandrel. The temperature of the part during the pouring ofthe bearing material is maintained at a temperature above the meltingpoint of the bearing material.

Thus, the billet is heated only a single time and the steps withinL-shaped box 21 are each carried out on the hot billet withoutintermediate cooling and reheating thereof.

Typical bearing materials utilized for track roller bearings includebronze. The particular temperature above which a track roller 10 shouldbe kept differs depending upon the particular composition of the bronzeor other bearing material which is utilized. For example, if the bronzeis 90% copper and 10% tin, the temperature should be kept above about1010° C. If the composition is 80% copper and 20% tin, the temperatureshould be kept above about 900° C. If the composition comprises 75%copper to 25% tin, the temperature should be kept above about 800° C. Toprevent local solidifaction of bearing material it is preferred that thetemperature be kept at least about 15° C above the melting point of thebearing material.

Generally, the hot machining and the pouring of hot molten materialabout a mandrel takes place at temperatures within the range from about650° to about 1500° C.

After the bearing has been cast in place within the bore 18 the trackroller 10 is generally but not invariably hardened by quenching inquenching step 30 as by plunging it into fluid and then is allowed tocool as in cooling step 32. After the part is cooled, the bearing can bemachined as illustrated at machine step 34, if desired, to a finisheddiameter, thereby leading to a finished part 36.

The bearing pouring apparatus 38 of the preferred embodiment of theinvention, along with the preferred embodiment of the mandrel 40 of thepresent invention, are illustrated in FIG. 3. The bearing pouringapparatus comprises an upright cylindrical base structure 42 upon whichone of the end surfaces 20 of the track roller 10 is placed in a closefitting, supporting relationship. A ring-like member 43 including anoverflow trough 44 is positioned upon the upper end surface 20 of thetrack roller to facilitate pouring and removal of molten material usedin casting the bearing 19. The mandrel includes at one end thereof ashaft 45 and at the other end thereof a head 46. The mandrel is loweredthrough aligned bores 47 of the ring-like member 43, bore 18 of thetrack roller 10, and bore 48 of the cylindrical base 42. The base bore48 is tapered to mate with a tapered end 50 of the head 46 to form arelatively fluid-tight joint therebetween and to center the mandrelrelative to the aligned bores 47, 18 and 48. The other end 52 of thehead 46, adjacent where the shaft 45 attaches thereto, the tapering ofthe tapered end 50 ceases and a bearing material heating section 51 ofthe mandrel is defined between the tapered end and the shaft portionsthereof. The diameter of the bearing material heating section of themandrel is such as to provide a space between it and the bore 18approximately equal to the thickness of the bearing which is to be casttherebetween.

Within the mandrel 40 adjacent the one end 54 thereof and in the taperedend 50 thereof are the cooling coils 56. Above the cooling coils,intermediate said cooling coils and the other end 52 of the tapered end50 (in the bearing material heating section 51) is the heating coil 58which typically is a conventional induction heating unit.

In operation, the mandrel 40 is inserted through the bores 47, 18 and 48until the tapered end 50 thereof binds within the bore 48. Then themolten bearing material, e.g., molten bronze, is poured as from theladle 60 into the space between the shaft 45 and the bore 18. Themandrel is then removed by impelling the shaft 45 upwardly. The heatingcoil 58 is kept at a high enough temperature so that the bearingmaterial thereadjacent remains molten. The cooling coils 56 are keptcooled enough so that the bearing material solidifies as the tapered end50 of the mandrel 40 passes opposite it. Thereby, due to the progressivecooling, the bearing material is solidified to bond it in place and makeit integral with the bore 18 from the bottom thereof upwardly as themandrel 40 is drawn upwardly through the bore and then finally out ofthe bore. Meanwhile, the excess molten material between the shaft 45 andthe bore is drawn upwardly by the other end 52 of the tapered end 50 ofthe mandrel, up into the ring-like member 43 and out of the trough 44for reuse. The relatively large mass of molten bronze in the bore aboutthe shaft 45 helps maintain the bronze in a molten state until themandrel is retracted from the bore.

While the invention has been particularly described with respect to usewith a track roller bearing, the process, product and apparatus of thepresent invention are also useful to provide other materials castintegrally within bores.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodification, and this application is intended to cover any variations,uses or adaptations of the invention following, in general, theprinciples of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains and as may be applied to the essentialfeatures hereinbefore set forth, and as fall within the scope of theinvention and the limits of the appended claims.

We claim:
 1. A process for forming a part including a bore with abearing integrally solidified in and bonded thereto, comprising:hotmachining a bore into a billet in a non-oxidizing atmosphere;introducing molten bearing material about a mandrel positioned in thebore with the bore being positioned generally vertically whilemaintaining the billet, the mandrel and the bearing material in thenon-oxidizing atmosphere; and drawing the mandrel upwardly from the borewhile cooling an end of the mandrel which exits the bore lastsufficiently to progressively solidify the bearing material adjacentsaid end of said mandrel as the mandrel is drawn through the materialand out of the bore and integrally solidify the bearing material in andbond it to the bore.
 2. A process as in claim 1, including as part ofsaid drawing and cooling step, heating the mandrel intermediate saidlast exiting end thereof and the other end thereof and therebyprogressively heating the bearing material just prior to cooling it asthe mandrel is drawn through the material and out of the bore.
 3. Aprocess as in claim 2, further characterized in that said billet ismaintained at a temperature above the melting point of said bearingmaterial during said introducing step.
 4. A process as in claim 3,wherein said hot machining is carried out on a billet maintained at atemperature above the melting point of said bearing material.
 5. Aprocess as in claim 1, wherein said hot machining and introducing stepsare carried out at a temperature which falls within the range from about650° to about 1500° C.
 6. A process as in claim 5, including as an addedstep after said drawing and cooling step:quenching the part in a fluidto adjust the hardness thereof.
 7. A process as in claim 5, including asan added step, prior to said hot machining step:forming said billet intothe shape of said part in said non-oxidizing atmosphere at saidtemperature which falls within the range from about 650° to about 1500°C.
 8. A part including a bore therethrough and a bearing integrallysolidified in and bonded to said bore, said part being produced inaccordance with the process of claim 1.